Apparatus for producing continuous round jacketed lightguides

ABSTRACT

An apparatus is provided for protectively jacketing a bundle of polymeric optical filaments which includes an extrusion device having guide means therewithin and an orifice so constructed and arranged so that a protective jacketing of polymeric material contacts and flows about said bundle of optical filaments advancing continuously through said extrusion device before said polymeric material flows through the orifice of said extrusion device.

United States Patent [1 1 Henrikson et al. 425/1 13 Hager Nov. 20, 1973APPARATUS FOR PRODUCING FOREIGN PATENTS OR APPLICATIONS CONTINUOUS ROUNDJACKETED 223,886 3/1958 Australia 425/113 LIGHTGUIDES 1,079,551 8/1967Great Britain 425/l13 I [75] Inventor Thomas C. Hager,Washington, W. Va.Primary Examiner-R. Spencer Annear [73] Assignee: E. l. du Pont deNemours and AnorMyTManln Levy Company, Wilmington, Del.

A l. N 4 98 v [21] pp 0 18 An apparatus is provided for protectivelyjacketing a Related App Data bundle of polymeric optical filaments whichincludes [60] Division of Ser. No. 043,701, June 5, 1970, Pat. No. anextrusion device having guide means therewithin 3,646,186, which is acontinuation-in-part of Sen: No. and an orifice so constructed andarranged so that a 1966, abandonedprotective jacketing of polymericmaterial contacts and flows about said bundle of optical filaments ad-[52] US. Cl 425/114, 425/466, 264/172 vancing continuously through saidextrusion device [51] Int. Cl. B291! 3/00, 1329f 3/00 beforg saidpolymeric material flows through the ori- I [5 8] Field of Search425/114, 466, 113; fi f id t i n d vi [56] References Cited 2 Clams 7Wing F'gures APPARATUS FOR PRODUCING CONTINUOUS ROUND JACKETEDLI'GHTGUIDES This application is adivision of U.S. patent applicationSer. No. 043,701, filed Jun. 5, 1970, now U.S. Pat. No. 3,646,186 whichis-a continuation-inpart of application U.S. Ser. No. 600,919, filedDec. 12, 1966, now abandoned.

This invention relates to the jacketing of continuous Zplastic opticalfilamentary material to produce a lightguide in which the filamentarymaterial is tightly jacketed and the jacket is round.

Plastic opticalfilamentary material is defined as being sheathed plasticfilaments or fibers which are capable of transmitting light over longstraight or curved lengths. Suitable plastic optical filamentarymaterial that can be used in the practice of this invention is describedin British PatentNo. 1,037,498, entitled Light Transmitting Filaments-.Tlie process=of this invention can be used to protectively jacketplastic optical filamentary material of any composition and diameter.

Thereare two general types of jacketing processes: pressure typeextrusion process and tubing type extrusion process. Both processes havebeen unsuccessful in producing lightguides in: which the plastic opticalfilamentary material is satisfactorily tightly jacketed and thejacketing is round The most seriousproblem in jacketing plasticfilamentary material is thattmany presently available opticalfilamentary materialsare heat sensitive to temperaturesabove 130C. Inextrusion jacketing processes, the extrudable jacketing: material is ata temperature well in excess-of 130C.-within the extruder. Thus, thejacketing material must not be allowed to remain in prolonged contactwith the plastic filaments within the extruder or degradation willoccur.

In a pressure type extrusion process, the filamentary material issubjected-to the high temperatures and pressures of the extrudablematerial for a sufficient period of time to cause such degradation.Thus, the maximum temperature limit of the" filamentary material iseasily exceeded. In addition, the pressure-type extrusion process couldnot be used to jacket a multistrand or bundle offilamentary materialbecause the bundle is not round andwould fail to seal the outlet of thefilament guide within the extruder whicli results in leakage of theextrudable material back into the filament guide.

In-a tubing-type extrusion process, the major probrem faced is thaton-extrusion of the plastictube, the inner diameter of theplastic tubeis larger than the outer diameter of the filamentary material whichresults in a loose fit. It is important that the filaments be heldfirmly at each endof the lightguide for efficient pick-up and display oflight. Lightguides prepared using a loose jacket require that the endsbe specially treated by potting or clamping to immobilize the ends. Thisproblem can be partially solved by stretching the tubing while it isbeing drawn down around the filamentary material, but this createsstresses in the tubing which cannot be relieved on a production linebasis due to the low 'heat'tolerance of the plastic filamentarymaterial. Due to these stresses, the tubing or jacket may later shrinkwhen subjected to in-service temperatures leaving the filamentarymaterial exposed and possibly yielding a: kinked lightguide. Anadditional problem is that the tubing, when stretched, takes the shapeof the bundle which may vary from oval toround-or from flat tolightguide product of substantially uniform diameter comprising thesteps of extruding a jacketing material through a die orifice having alandup to 20 mils in length from an annular section of a melt reservoirdefined by a melt chamber and the exterior surface of a filament guideto form a tube, the filament guide terminating spaced from said orificeand within the reservoir, the outer diameter of said tube being formedon the die orifice, and

simultaneously within said tube and while said tube is forming passingone or more polymeric optical filaments through the filament guide, andpassing gas through said filament guide to cool the optical filaments insaid guide, and

prior to passing said optical filaments through said guide adjusting thespacing between the end of said filament guide and said orifice anamount defined by a Y factor of 6-40 percent where Y [(bundle O.D.Tubing I.D.)/bundle O.D.] X 100,

whereby in the space defined by the dieorifice and theterminus of thefilament guide jacketing material passes about and is in intimatecontact with said optical filaments; and passing said jacketedlightguides through said die to form a uniform outside diameter on saidmaterial with a second polymeric material whereby the first material isexposed for only short duration to elevated temperature and whichprotectively jacketed product has a substantially uniform outsidediameter, said apparatus comprising means for introducing said secondpolymeric material to a melt reservoir,

a melt reservoir,

a die orifice,

a tubular filament guide member,

said melt reservoir containing therein said tubular filament guidemember axially. disposed with saidreservoir and spaced from said dieorifice,

saidtubular member on the end disposed toward said orifice havingconverging configuration on its exterior surface, and the inner walls ofsaid melt reservoir in the region of said orifice forming a convergingsurface, the converging surfaces of said reservoir and said tubularmember forming a converging annular passage for the flow of said secondpolymeric material,

the inner surface of said tubular member disposed to receive opticalfilamentary material from outside said chamber at its end opposite tothat disposed-to thedie orifice and the inner surface of said tubularmember disposed to receive and discharge cooling gas, the end of saidtubular member disposed toward said orifice being spaced therefrom in anamount defined by a Y factor 6 to 40 percent where Y [(bundle O.D.tubing I.D.)/bundle O.D.] X 100 said orifice having a land of from O to20 mils, whereby the second polymeric material passing around saidtubular member flows about polymeric optical filaments of said firstpolymeric material in the space between the end of tubular member andsaid orifice before being extruded through said die to form aprotectively jacketed light guide of substantially uniform diameter.Preferably Y is between 15% and 28%.

This and other embodiments of this invention will be hereinafterdescribed with reference to the following numbered drawings:

FIG. 1 shows a schematic end elevation of an extruder cross-head;

FIG. 2 shows an enlarged section of FIG. 1 taken on line 22;

FIG. 3A shows an enlarged section of the die andfilament guide of FIG. 2producing a plastic tubing;

FIG. 3B shows the section of the die and filament guide of FIG. 3A as abundle of plastic optical filaments are being fed through the filamentguide;

FIG. 3C shows the section of the die and filament guide of FIG. 3B withthe bundle of plastic optical filaments completely filling the plastictubing;

FIG. 4 shows an enlarged cross-section of a bundle of plastic opticalfilaments;

FIG. 5 shows an enlarged cross-section of the finished lightguide ofthis invention in which the bundle of plastic optical filaments arejacketed in a protective plastic jacket.

Referring to the drawings, FIG. 2 shows an extruder cross-head 1including structure defining an extrudate chamber 6, a circular die 4 atone end of the chamber and a tubular filament guide 12 extendinglongitudinally within the chamber. The die 4 has an outer or die face 8and an inner face of a uniformly converging surface 9 which terminatesinto the die face 8 to form an orifice 2. The filament guide 12 hasthreads 19 designed to engage a fixed nut 22 and is adjustable along itslongitudinal axis which intersects the center of orifice 2, by screwingthe filament guide into or out of the tubular filament guide 12 has afilament outlet 14 which communicates with the extrudate chamber 6 andis recessed from the die face, a filament inlet 15 which communicateswith the atmosphere, and a filament tube 18, which longitudinallydivides the interior of the filament guide into art-inner chamber 17 anda concentric outer chamber 16. The filament tube 18 has holes 13 thereinwhich allow chambers 16 and 17 to communicate. Chamber 16 is connectedto a source of suction (not shown) through valve 24 to produce a vacuumwithin the inner chamber 17 by withdrawing air from chamber 16 slightlyfaster than it can enter chamber 17 through inlet 15.

As shown in FIG. 3A, molten extrudate is received from an extruder (notshown) by extrudate chamber 6, and the extrudate flows around thetapered end of the filament guide 12 and out orifice 2 in the form of atubing 11. The filament guide 12 is longitudinally adjusted within theextrudate chamber so that the outlet is recessed from the die face 8sufficiently to produce an inner diameter of tubing [I.D. in Equation I]which is less than the outer diameter as hereinafter defined of theoptical filamentary material to be jacketed with the tubing.

The outer diameter of filamentary material of irregular cross-sectioncan be considered as the outer diameter of an equivalent essentiallycircular area.

The filamentary material in the form of a bundle 10 of optical filamentsis passed through the inner chamber 17 or filament tube 18 of thefilament guide 12 and into the interior of tubing 11 as is shown in FIG.3B. Upon continuing passage of the bundle 10 through the filament 12 andextrusion of the tubing 11, the entire interior of the tubing becomesoccupied with the bundle as shown in FIG. 3C.

The spacing between the tip of the filament guide and the die orifice isadjusted such that Y as defined by Equation I below is between 6 to 40percent and preferably 15 to 28 percent.

Y= [(bundle O.D. Tubing I.D.)/bundle O.D.] X

all terms as hereinbefore defined.

The tubing I.D. as discussed with relation to FIG. 3A is the innerdiameter of a tubing jacket extruded through the equipment at a givenspacing of filament guide to die orifice without the presence of thefilaments to be protectively jacketed.

The vacuum present within the filament guide 12 maintains the intimatecontact between the bundle l0 and tubing 11 obtained within the die asthe tubularly jacketed bundle leaves the die 4. The vacuum also improvespentration of the extrudate melt into the bundle within the die toimprove the tightness of fit. In addition, the vacuum produces a coolingeffect on the bundle and filament tube 18, by movement of air throughchambers 16 and 17 as above described.

The intimate contact between bundle l0 and tubing 11 obtained within thedie dispenses with the need for any substantial amount of drawing of thetubing after it leaves the die. Thus, stresses are not created in thetubing to the extent that such stresses might later, in service, berelieved, causing kinking of the lightguide and relative movementbetween optical filaments and tubing (protective jacketing material).

The optical filamentary material to be jacketed by the process of thisinvention can be in the form of a single filament or a bundle thereof,i.e., more than one filament running contiguously with one another.Generally, the filaments of the bundle will be untwisted with respect toeach other, resulting in a bundle of irregular cross-section, a factorwhich makes the extrudate melt backwards flow problem particularlyacute, but which is overcome by the process of the present invention.

FIG. 4 shows a cross-section of a bundle 10 of untwisted optic filaments30 which can be passed through the filament guide 12 for jacketingaccording to the present invention. This figure also shows theirregularity of the cross-sectional outline of the bundle.

In FIG. 5, the bundle 10 of FIG. 4 is shown with a tight protectiveplastic jacket of tubing 11 applied according to the present invention.The cross-sectional outline (outer surface) of the tubing is round,despite the irregular outline of the bundle 10. The tubing 11 haspenetrated the bundle l rendering its filaments,

present between the die face and the converging surface in order tominimize orifice wear. As this land is increased, so does back pressure.Consequently, as small a land as possible should be used in carrying outfor practical purposes, immobile with respect to one the process of thisinvention. Exemplary of the amount another and to the tubing. Inaddition, the bundle 10 is of land that can be used is land up to 20mils wide (diswell centered within the tubing. tance between die face atorifice and converging sur- Suitable materials for use in ja ketingOptical filaface at orifice) which gives an orifice of correspondingmentary material by the process of the present invenl th, tion are anyof those materials which are extrudable 10 The outer diameter offilamentary material of irreguinto a tubing under the conditionshereinbefore d lar cross-section can be considered as the outerdiamescribed without degrading the particular filamentary ter of anequivalent essentially circular area. material being used as a core andwhich have a protec- E A P E tive quality for the filamentary material.The jacketing x M L S material Should be non-reactive, in the se thatthe A number of runs were made according to the followoptical quality ofthe filamentary material is adversely ing general procedure: Anadjustable filament guide effected, with the optical filamentarymaterial during and die disigned and fabricated as above-describedjacketing and subsequent use. Examples of suitable were installed in astandard extruder cross-head with jacketing materials include naturaland synthetic rubthe filament guide outlet recessed from the die face toher and a-monoolefin polymers and copolymers, such produce an extrudedtubing having an inner diameter as polyethylene, preferably having lowor medium densmaller than the outer diameter of the optical-filamensity,and polypropylene, and vinyl chloride polymers tary material to bejacketed. The filament guide was and copolymers each containingnon-migratory plastilongitudinally adjusted in order to vary theinterference cize rs. fit and jacket thickness. Then the opticalfilamentary Preferably, the conyerging surface 9 of the die 4termaterial was passed through the filament guide and was minates at thedie face .8, as shown in FIG. 2, in order jacketed with tubing. Detailsof these runs are given in that outlet of the filament guide 12 can bepositioned the following Table. The optical filamentary material in asclosely as possible to the die face, yet recessed thereruns l-l 3 ispolymethylmethacrylate sheathed in a from to produce the fit betweendesired protective fluoroalkyl methacrylate polymer as described inButjacketing tubing 11 and the optical filamentary matesh Pat. No.1,037,498, and 1n run 14 1s polystyrene rial. A small amount of landdefining orifice 2 may be sheathed m polymethylmethacrylate- TABLE I(MATERIALS) Optical filamentary material Jacket material Bundle NoFilament outer filadiameter diameter Density Melt Durometer Run No ments(mils) (mils) Material at 23 0. index hardness 16 i0 Polyvinylchloride". 1. 20 A scale, 82. 16 10 45 -.d 1.20 Ascale, 82. 32 10 1.37 Cscale, 79. 10 10 0.917 4.0 10 10 0.917 4.0 16 10 0.905 4.3 16 10 0.9051.5 43 10 0.930 3.0 64 10 o 0. 930 3.0 32 10 65 Polyvinyl chloride 1. 20A scale, 82

4 20 47 Polyethylene 0. 930 3. 0 1 20 20 d 0. 930 3.0 1 30 0.930 3.0 1010 0. 930 3.0

' Nitrile rubber plasticizer. Polymeric polyester plasticizer.

TABLE II (CONDITIONS AND RESULTS) Melt temp. Linear Filament of jacketjacketing Jacket Diameter guide Intermaterial rate thickness of productoutlet size Die orifice terence Vacuum C (f.p.m.) (mils) (mils) (mils)size (mils) (mils) (in. of Hg) 147 89 20 86 55 95 10 7 150 296 20 86 5586 10 7 167 99 20 110 110 14 7. 5 150 50 20 88 55 86 10 7.5 152 10s 20as 55 10 7. 5 199 91 20 86 55 86 10 e 192 20 as 55 80 10 7 163 111 20110 00 1s 8 159 20 130 105 125 20 1s. 3 14s 80 15 100 76 103 14 10 157200 20 as 55 a0 10 15 181 153 10 40 30 52 5 7.1-1 173 29 85 45 86 5 10.2 103 13s 20 as 55 86 10 12. s

As many apparently widely different embodiments of this invention may bemade without departing from the spirit of scope thereof, it is to beunderstood that this invention is not limited to the specificembodiments thereof except as defined in the appended claims.

I claim:

1. Apparatus for protectively jacketing optical filaments of a firstpolymeric material with a second polymeric material whereby the firstmaterial is exposed for only short duration to elevated temperature andwhich protectively jacketed product has a substantially uniformdiameter, said apparatus comprising means for introducing said secondpolymeric material to a melt reservoir,

a melt reservoir,

a die orifice,

a tubular filament guide member comprising an inner axial member and anouter member forming an inner chamber surrounded by a concentric outerchamber,

said melt reservoir containing therein said tubular filament guidemember axially disposed with said reservoir and spaced from said dieorifice,

said tubular member on the end disposed toward said orifice havingconverging configuration on its exterior surface, and the inner walls ofsaid melt reservoir in the region of said orifice forming a convergingsurface, the converging surfaces of said reservoir and said tubularmember forming a converging annular passage for the flow of said secondpolymeric material,

the inner surface of said tubular member disposed to receive opticalfilamentary material from outside said chamber at its end opposite tothat disposed to the die orifice and the inner surface of said tubularmember disposed to receive and discharge cooling the end of said tubularmember disposed toward said orifice being spaced therefrom in an amountdefined by a Y factor 6 to 40 percent, where Y [(bundle O.D. tubingI.D.)/bundle O.D.] X

said orifice having a land of from O to 20 mils, whereby the secondpolymeric material passing around said tubular member flows aboutpolymeric optical filaments of said first polymeric material in thespace between the end of tubular member and said orifice before beingextruded through said die to form a protectively jacketed lightguide ofsubstantially uniform diameter.

2. Apparatus of claim 1 wherein Y is between 15 percent and 28 percent.

1. Apparatus for protectively jacketing optical filaments of a firstpolymeric material with a second polymeric material whereby the firstmaterial is exposed for only short duration to elevated temperature andwhich protectively jacketed product has a substantially uniformdiameter, said apparatus comprising means for introducing said secondpolymeric material to a melt reservoir, a melt reservoir, a die orifice,a tubular filament guide member comprising an inner axial member and anouter member forming an inner chamber surrounded by a concentric outerchamber, said melt reservoir containing therein said tubular filamentguide member axially disposed with said reservoir and spaced from saiddie orifice, said tubular member on the end disposed toward said orificehaving converging configuration on its exterior surface, and the innerwalls of said melt reservoir in the region of said orifice forming aconverging surface, the converging surfaces of said reservoir and saidtubular member forming a converging annular passage for the flow of saidsecond polymeric material, the inner surface of said tubular memberdisposed to receive optical filamentary material from outside saidchamber at its end opposite to that disposed to the die orifice and theinner surface of said tubular member disposed to receive and dischargecooling gas, the end of said tubular member disposed toward said orificebeing spaced therefrom in an amount defined by a Y factor 6 to 40percent, where Y ((bundle O.D. - tubing I.D.)/bundle O.D.) X 100 saidorifice having a land of from 0 to 20 mils, whereby the second polymericmaterial passing around said tubular member flows about polymericoptical filaments of said first polymeric material in the space betweenthe end of tubular member and said orifice before being extruded throughsaid die to form a protectively jacketed lightguide of substantiallyuniform diameter.
 2. Apparatus of claim 1 wherein Y is between 15percent and 28 percent.